Micro-electromechanical systems (MEMS) devices have a wide variety of applications and are prevalent in commercial products. One type of MEMS device is a MEMS RF switch. A typical MEMS RF switch includes one or more MEMS switches arranged in an RF switch array. MEMS RF switches are ideal for wireless devices because of their low power characteristics and ability to operate in radio frequency ranges. MEMS RF switches are often found in cellular telephones, wireless computer networks, communication systems, and radar systems. In wireless devices, MEMS RF switches can be used as antenna switches, mode switches, and transmit/receive switches.
MEMS RF switches typically implement cantilever beam switching mechanisms, for example conductive beam and the insulated beam). The actuator capacitor of the switch is formed between a conductive plate of the cantilever beam and a control electrode that runs under the beam. When a voltage is applied to the control electrode, an electric field develops between the two plates.
The force of this electric field bends the cantilever beam down. When the beam deforms far enough, the switch makes contact, and is “closed”. The voltage that closes the switch is called V pull-in (VPI). Often a larger voltage than VPI is desirable to increase contact pressure and reduce contact resistance.
To de-actuate the switch, the voltage across the actuation capacitor drops below significantly below VPI. There is inherent hysteresis between the actuation voltage and the de-actuation voltage. For instance, for a switch that has a actuator gap change from open to closed of gfinal<(⅔) g0, the de-actuation voltage will be approximately ⅓ the actuation voltage. Once the switch is actuated, the actuation capacitor voltage can leak down significantly, and the switch will remain closed. The hysteresis however slows down de-actuation to open the switch.